Method for producing a methane-rich stream and a c2+ hydrocarbon-rich stream, and associated equipment

ABSTRACT

The second expanded fraction (91A) from the second dynamic expansion turbine (40) is used to form a cooled reflux stream (91B) injected into the column (30).

The present invention relates to a method for producing a methane-richstream and a C₂ ⁺ hydrocarbon-rich stream from a feed stream containinghydrocarbons, of the type comprising the following steps:

-   -   separating the feed stream into a first fraction of the feed        stream and at least one second fraction of the feed stream;    -   cooling the first fraction of the feed stream in a first heat        exchanger;    -   injecting the first fraction of the cooled feed stream in a        first separating flask to produce a light head stream and a        heavy bottoms stream;    -   expanding a turbine feed fraction formed from the light head        stream in a first dynamic expansion turbine up to a first        pressure and injecting at least part of the first expanded        fraction coming from the first turbine into a first distillation        column;    -   expanding at least part of the heavy bottoms stream to form an        expanded bottoms stream and injecting the expanded bottoms        stream into the first distillation column without going through        the first heat exchanger between the first separating flask and        the first distillation column;    -   recovering a bottoms stream at the bottom of the first        distillation column, the C₂ ⁺ hydrocarbon-rich stream being        formed from the column stream;    -   recovering and heating a methane-rich overhead stream;    -   compressing at least one fraction of the overhead stream in at        least a first compressor coupled to the first dynamic expansion        turbine and in at least one second compressor;    -   forming a methane-rich stream from the heated and compressed        overhead stream.

Such a method is intended to extract C₂ ⁺ hydrocarbons, such as inparticular ethylene, ethane, propylene, propane and heavierhydrocarbons, in particular from natural gas, refinery gas or syntheticgas obtained from other hydrocarbonaceous sources such as coal, raw oil,or naphtha.

Natural gas generally contains a majority of methane and ethane makingup at least 50% by moles of the gas. It also contains a more negligiblequantity of heavier hydrocarbons, such as propane, butane, pentane. Incertain cases, it also contains helium, hydrogen, nitrogen and carbondioxide.

It is necessary to separate the heavier hydrocarbons from the naturalgas to respond to at least two imperatives.

First, economically, C₂ ⁺ hydrocarbons, and especially ethane, propaneand butane, can be exploited. Furthermore, the demand for natural gasliquids as feeds for the petrochemical industry is continuouslyincreasing and should continue to increase in the coming years.

Furthermore, for method reasons, it is desirable to separate the heavyhydrocarbons so as to prevent them from condensing during transportand/or manipulation of the gases. This makes it possible to avoidincidents such as the arrival of liquid plugs in transport or treatmentequipment designed for gas effluents.

To separate the C₂ ⁺ hydrocarbons from the natural gas, it is known touse an oil absorption method that makes it possible to recover up to 90%of the propane and up to about 40% of the ethane.

To achieve higher recovery rates, cryogenic expansion methods are used.

In one known cryogenic expansion method, part of the feed streamcontaining the hydrocarbons is used for the secondary reboilers of asplitter of the methane.

Then, the different effluents, after partial condensation, are combinedto feed a gas-liquid separator.

As described in U.S. Pat. No. 5,555,748, the light stream obtained atthe head of the separator is divided into a first column feed fraction,which is condensed before being sent toward the head feed of thedistillation column and a second fraction that is sent toward a dynamicexpansion turbine before being injected into the distillation column.

This method has the advantage of being easy to start and offeringsignificant working flexibility, combined with good effectiveness andgood safety.

However, economic constraints require further increasing theeffectiveness of the method while preserving a very high methaneextraction output. It is also necessary to minimize the bulk of theequipment and to reduce, or even eliminate the contribution of outsiderefrigerants such as propane, in particular to implement the method onfloating equipment or in safety-sensitive areas.

One aim of the invention is therefore to obtain a production method thatmakes it possible to separate a feed stream containing hydrocarbons intoa C₂ ⁺ hydrocarbon-rich stream and a methane-rich stream, veryeconomically, with a small bulk, and very effectively.

To that end, the invention relates to a method of the aforementionedtype, characterized in that the method comprises the following steps:

-   -   expanding at least part of the second fraction of the feed        stream in a second dynamic expansion turbine, separate from the        first dynamic expansion turbine, up to a second pressure, to        form a second expanded fraction coming from the second dynamic        expansion turbine, the second pressure being substantially equal        to the first pressure; and    -   cooling and at least partially liquefying at least part of the        second expanded fraction coming from the second dynamic        expansion turbine to form a cooled reflux stream in the first        distillation column.

The method according to the invention can comprise one or more of thefollowing features, considered alone or according to all technicallypossible combinations:

-   -   the pressure difference between the first pressure and the        second pressure is less than 8 bars;    -   the temperature of the part of the second fraction of the feed        stream injected into the second dynamic expansion turbine is        higher than the temperature of the turbine feed fraction        injected into the first dynamic expansion turbine;    -   the method includes the injection of the first expanded fraction        from the first dynamic expansion turbine into a second heat        exchanger to be cooled and partially liquefied therein, the        first cooled expanded fraction forming an additional cooled        reflux stream, the method including the injection of the        additional cooled reflux stream into the first distillation        column;    -   the method comprises the following steps:        -   injecting the second expanded fraction coming from the            second dynamic expansion turbine into a downstream            separating flask to form a second gas head stream and a            second liquid bottoms stream,        -   cooling the second gas head stream to form a cooled reflux            stream,        -   injecting at least part of the second expanded fraction from            the second dynamic expansion turbine into an auxiliary            column, and        -   forming a cooled reflux stream from the bottoms stream of            the auxiliary column;        -   possibly, partially condensing the second fraction of the            feed stream;        -   injecting the second fraction of the feed stream into an            upstream separating flask to form a second gas fraction and            a second liquid fraction;        -   injecting the second gas fraction into the second dynamic            expansion turbine;        -   injecting the second liquid fraction, after expansion, into            a lower part of the first distillation column;    -   the entire second fraction of the feed stream is injected into        the second dynamic expansion turbine, possibly without cooling        between the step for separating the feed stream and the step for        injecting the second fraction of the feed stream into the second        dynamic expansion turbine;    -   the method includes the following steps:        -   removing a secondary compression fraction in the            methane-rich overhead stream, before the passage of a            fraction of the methane-rich overhead stream in the first            compressor,        -   passage of the secondary fraction in a third compressor            coupled to the second dynamic expansion turbine;        -   injecting the compressed secondary fraction from the third            compressor into the fraction of the compressed overhead            stream, downstream of the first compressor;    -   the second compressor comprises a first compression stage, at        least one second compression stage, and a refrigerant inserted        between the first compression stage and the second compression        stage, the method including a step for passage of the compressed        overhead stream from the first compressor successively in the        first compression stage, the refrigerant, then the second        compression stage;    -   at least part of the second expanded fraction from the second        dynamic expansion turbine, at least one fraction of the overhead        stream, and possibly the first expanded fraction from the first        dynamic expansion turbine, are placed in a heat exchange        relationship;    -   the method comprises the following steps:        -   dividing the light head stream into the turbine feed            fraction and a column feed fraction;        -   cooling and at least partially condensing the column feed            stream in a second heat exchanger,        -   expanding and at least partially injecting the cooled column            feed fraction into the first distillation column,    -   at least part of the second expanded fraction from the second        dynamic expansion turbine and the column feed fraction        advantageously being placed in a heat exchange relationship;    -   at least a fraction of the overhead stream and at least one part        of the second expanded fraction from the second dynamic        expansion turbine are placed in a heat exchange relationship in        a downstream heat exchanger separate from the second heat        exchanger;    -   the method comprises the following steps:        -   removing a bleed stream from the overhead stream;        -   cooling the bleed stream at least in the first heat            exchanger and injecting the cooled bleed stream into the            first distillation column; and        -   possibly, heat exchange of the bleed stream with at least            part of the second expanded fraction from the second            turbine.    -   the method includes the following steps:        -   removing a reboiling stream in the first distillation column            at a removal level;        -   putting the reboiling stream in a heat exchange relationship            with at least part of the second expanded fraction coming            from the second dynamic expansion turbine to cool and at            least partially liquefy the part of the expanded second            fraction coming from the second dynamic expansion turbine;            and        -   possibly, placement in a heat exchange relationship with the            first expanded fraction from the first turbine;        -   reinjecting the reboiling stream into the first distillation            column at a level below the removal level.    -   the method includes the following steps:        -   removing an extra cooling stream from the methane-rich            overhead stream or from the stream formed from the            methane-rich overhead stream;        -   expanding and injecting the expanded extra cooling stream            into a stream circulating upstream of the first expansion            turbine, advantageously in the first fraction of the cooled            feed stream or in the turbine feed fraction;    -   the method comprises the following steps:        -   passage of the methane-rich overhead stream in the first            heat exchanger;        -   removal of an auxiliary expansion stream in the methane-rich            overhead stream, after its passage in the first heat            exchanger;        -   dynamic expansion of the auxiliary expansion stream in an            auxiliary dynamic expansion turbine; and        -   injecting the expanded stream from the auxiliary dynamic            expansion turbine into the methane-rich overhead stream,            before its passage in the first heat exchanger.

The invention also relates to equipment for producing a methane-richstream and a C₂ ⁺ hydrocarbon-rich stream from a feed stream containinghydrocarbons, of the type comprising:

-   -   means for separating the feed stream into a first fraction of        the feed stream and at least one second fraction of the feed        stream;    -   a first heat exchanger to cool the first fraction of the feed        stream;    -   means for injecting the first cooled feed fraction into a first        separating flask to produce a light head stream and a heavy        bottoms stream;    -   a first dynamic expansion turbine and means for injecting a        turbine feed fraction formed from the light head stream into the        first dynamic expansion turbine so as to expand the turbine feed        fraction up to a first pressure;    -   a first distillation column;    -   means for injecting at least part of the first expanded fraction        into the first turbine in the first distillation column;    -   means for expanding at least part of the heavy bottoms stream to        form an expanded bottoms stream and means for injecting at least        part of the expanded bottoms stream into the first distillation        column, the means for injecting the expanded bottoms stream        being configured so that the bottoms stream does not pass        through the first heat exchanger between the first separating        flask and the first distillation column;    -   means for recovering a bottoms stream at the bottom of the first        distillation column, the C₂ ⁺ hydrocarbon-rich stream being        formed from the bottoms stream;    -   means for recovering and heating a methane-rich overhead stream,    -   at least one first compressor coupled to the first dynamic        expansion turbine and at least one second compressor to compress        at least one fraction of the overhead stream;    -   means for forming a methane-rich stream from the heated and        compressed overhead stream from the second compressor;    -   characterized in that the equipment comprises:        -   a second dynamic expansion turbine, separate from the first            dynamic expansion turbine,        -   means for injecting at least part of the second fraction of            the feed stream into the second dynamic expansion turbine to            form a second expanded fraction from the second dynamic            expansion turbine at a second pressure, the second dynamic            expansion turbine being arranged so that the first pressure            is substantially equal to the second pressure; and        -   means for cooling and at least partially liquefying at least            part of the second fraction from the second dynamic            expansion turbine to form a cooled reflux stream and means            for injecting the cooled reflux stream into the first            distillation column.

The equipment according to the invention can comprise the followingfeature:

-   -   the equipment comprises:    -   an auxiliary column;    -   means for injecting at least part of the second expanded        fraction from the second dynamic expansion turbine into the        auxiliary column; and    -   means for forming the cooled reflux stream from the bottoms        stream of the auxiliary column.

The invention will be better understood upon reading the followingdescription, provided solely as an example, and done in reference to theappended drawings, in which:

FIG. 1 is a summary flowchart of a first piece of production equipmentintended to implement a first method according to the invention;

FIG. 2 is a summary flowchart of a second piece of production equipmentintended to implement a second method according to the invention;

FIG. 3 is a summary flowchart of a third piece of production equipmentintended to implement a fifth method according to the invention;

FIG. 4 is a summary flowchart of a fourth piece of production equipmentintended to implement a sixth method according to the invention;

FIG. 5 is a summary flowchart of a fifth piece of production equipmentintended to implement a seventh method according to the invention;

FIG. 6 is a summary flowchart of a sixth piece of production equipmentintended to implement an eighth method according to the invention.

In all of the following, the same references will be used to designate astream circulating in a pipe and the pipe transporting it.

Furthermore, unless otherwise indicated, the cited percentages are molarpercentages and the pressures are given in absolute bars.

In the digitally simulated examples, the output of each compressor ischosen to be 82% polytropic and the output of each turbine is 85%adiabatic.

Likewise, the distillation columns described use plates, but they canalso use bulk or structured trim. A combination of plates and trim isalso possible. The additional turbines described drive compressors, butthey can also drive variable-frequency electric generators whereof theelectricity produced can be used in the network via a frequencyconverter. The streams whereof the temperature is higher than theambient temperature are described as being cooled by aero-refrigerants.Alternatively, it is possible to use water exchangers, for example usingfresh water or seawater.

FIG. 1 illustrates a first piece of production equipment 10 forproducing a methane-rich stream 12 and a C₂ ⁺ hydrocarbon-rich fraction14 according to the invention, from a feed gas stream 16.

The gas stream 16 is a natural gas stream, a refinery gas stream, or asynthetic gas stream obtained from a hydrocarbonaceous source such ascoal, raw oil, or naphtha. In the example illustrated in the Figures,the stream 16 is a dehydrated natural gas stream.

The method and equipment 10 advantageously apply to the construction ofa new methane and ethane recovery unit.

The equipment 10 comprises, from upstream to downstream, a first heatexchanger 20, a first separating flask 22, and a first dynamic expansionturbine 26, capable of producing work during the expansion of a streampassing through the turbine.

According to the invention, the equipment 10 also comprises a secondheat exchanger 28, a first distillation column 30, a first compressor 32coupled to the first dynamic expansion turbine 26, a first refrigerant34, a second compressor 36, a second refrigerant 38, and a bottoms pump39.

According to the invention, the equipment 10 also comprises a seconddynamic expansion turbine 40 and a third compressor 41 coupled to thesecond dynamic expansion turbine 40.

A first production method according to the invention, implemented in theequipment 10, will now be described.

As an example, the feed stream 16 is made up of a dehydrated natural gasthat comprises, in moles, 2.06% nitrogen, 83.97% methane, 6.31% ethane,3.66% propane, 0.70% isobutane, 1.50% n-butane, 0.45% isopentane, 0.83%n-pentane, and 0.51% carbon dioxide.

The feed stream 16 more generally has, in moles, between 5 and 15% of C₂⁺ hydrocarbons to be extracted and between 75 and 90% methane.

“Dehydrated gas” refers to a gas whereof the water content is as low aspossible and is in particular lower than 1 ppm.

The feed stream 16 has a pressure greater than 35 bars, in particulargreater than 50 bars and a temperature close to the ambient temperature,and in particular substantially equal to 30° C. The flow rate of thefeed stream is in this example 15,000 kmoles/hour.

The feed stream 16 is first divided into a first feed stream fraction41A and a second feed stream fraction 41B.

The ratio of the molar flow rate of the first fraction 41A to the secondfraction 41B is for example greater than 2, and is in particularcomprised between 2 and 15.

In the illustrated example, the first fraction 41A is injected into thefirst heat exchanger 20, where it is cooled and partially condensed toform a cooled feed stream fraction 42.

The temperature of the fraction 42 is below −10° C. and is in particularequal to −26.7° C. Then, the cooled fraction 42 is injected into thefirst separating flask 22.

The liquid content of the cooled fraction 42 is less than 50% molar.

A light gas head stream 44 and a heavy liquid bottoms stream 45 areextracted from the first separating flask 22.

In this example, the gas stream 44 is divided into a minority feedstream fraction 46 and a majority turbine feed fraction 48. The ratio ofthe molar flow rate of the majority fraction 48 to the minority fraction46 is greater than 2.

The column feed fraction 46 is injected into the second heat exchanger28 to be completely liquefied and sub-cooled therein. It forms a cooledcolumn feed fraction 49. This fraction 49 is expanded in a first staticexpansion valve 50 to form an expanded fraction 52 injected in refluxinto the first distillation column 30.

The temperature of the expanded fraction 52 obtained after passage inthe valve 50 is less than −70° C., and is in particular equal to −111°C. The pressure of the expanded fraction 52 is also substantially equalto the working pressure of the column 30, which is less than 40 bars andin particular comprised between 10 bars and 30 bars, advantageouslyequal to 17 bars.

The fraction 52 is injected into an upper part of the column 30 at alevel N1, situated at the first stage starting from the top of thecolumn 30.

The turbine feed fraction 48 is injected into the first dynamicexpansion turbine 26. It undergoes a dynamic expansion up to a pressureP1 close to the working pressure of the column 30 to form a firstexpanded feed fraction 54 that has a temperature below −50° C., inparticular equal to −79° C.

The expansion of the feed fraction 48 in the first turbine 26 makes itpossible to recover 3574 kW of energy that cool the fraction 48.

The first expanded fraction 54, which is the effluent resulting from thefirst dynamic expansion turbine 26, makes up a first cooled refluxstream 56.

The liquid content of the cooled reflux stream 56 is greater than 5%molar. The cooled reflux stream 56 is injected into a middle part of thecolumn 30 situated under the upper part, at a level N2 lower than thelevel N1, and in this example corresponding to the sixth stage startingfrom the top of the column 30.

The liquid heavy stream 45 recovered at the bottom of the separatingflask 22 is expanded in a second static expansion valve 58 to form anexpanded heavy stream 60.

The pressure of the expanded heavy stream 60 is less than 50 bars, andis in particular substantially equal to the pressure of the column 30.The temperature of the expanded heavy stream 60 is less than −30° C.,and is in particular substantially equal to −48° C.

The liquid heavy stream 45 is completely injected into the column 30after its expansion in the valve 58, without passing through the firstheat exchanger 20. In this way, the liquid heavy stream 45, beforepassing in the valve 58, and the expanded heavy stream 60 do not enterinto a heat exchange relationship with the feed stream 16, or with thefractions 41A, 41B of said feed stream 16.

In particular, the heavy stream 45 does not pass into the heat exchanger20 between the output of the separating flask 22 and the input of thecolumn 30.

A first reboiling stream 74 is removed near the bottom of the column 30at a temperature above −3° C., and in particular substantially equal to9.6° C., at a level N6 situated below the level N3, advantageously atthe twenty-first stage starting from the top of the column 30.

The first stream 74 is brought up to the first heat exchanger 20, whereit is heated to a temperature above 3° C., and in particular equal to16.3° C., before being sent back to a level N7 corresponding to thetwenty-second stage starting from the top of the column 30.

A second reboiling stream 76 is removed at a level N8 situated above thelevel N6 and below the level N3, advantageously at the seventeenth stagestarting from the top of the column. The second reboiling stream 76 isinjected into the first heat exchanger 20 to be heated therein up to atemperature above −8° C., and in particular equal to −4.1° C. It is thenreturned to the column 30 at a level N9 situated below the level N8 andabove the level N6, advantageously at the eighteenth stage starting fromthe top of the column 30.

A third reboiling stream 78 is removed a level N10 situated under thelevel N3 and above the level N8, advantageously at the thirteenth stagestarting from the top of the column 30. The third reboiling stream 78 isthen brought up to the first heat exchanger 20, where it is heated to atemperature above −30° C., and in particular equal to −19° C., beforebeing returned to a level N11 of the column 30 situated under the levelN10 and situated above the level N8, advantageously at the fourteenthstage starting from the top of the column 30.

In this way, the stream 52 is injected into the upper part of the column30, which extends from a height greater than 35% of the height of thecolumn 30, while the stream 60 is injected into a middle part thatextends under the upper part.

The column 30 produces a liquid bottoms stream 82 at the bottom. Thebottoms stream 82 has a temperature above 4° C., and in particular equalto 16.3° C. In this way, the bottoms stream 82 contains, by moles, 1.17%carbon dioxide, 0.00% nitrogen, 0.43% methane, 42.89% ethane, 28.40%propane, 5.51% i-butane, 11.66% n-butane, 3.47% i-pentane, and 6.46%n-pentane.

More generally, the stream 82 has a ratio C₁/C₂ less than 3% molar, forexample equal to 1%.

The stream 82 contains more than 80%, advantageously more than 87% bymoles of the ethane contained in the feed stream 16, and it containssubstantially 100% by moles of the C₃ ⁺ hydrocarbons contained in thefeed stream 16.

The bottoms stream 82 is pumped into the pump 39 to form the C₂ ⁺hydrocarbon-rich fraction 14.

It can advantageously be heated by putting it in a heat exchangerelationship with at least one fraction of the feed stream 16 up to atemperature below its boiling temperature, to keep it in liquid form.

The column 30 produces, at the head thereof, a methane-rich overhead gasstream 84. The stream 84 has a temperature below −70° C., and inparticular substantially equal to −105° C. It has a pressuresubstantially equal to the pressure of the column 30, for example equalto 17.0 bars.

The head stream 84 is successively injected into the second heatexchanger 28, then into the first heat exchanger 20 to be heated thereinand form a heated methane-rich head stream 86. The stream 86 has atemperature above −10° C., and in particular equal to 22.9° C.

At the output of the first exchanger 20, the stream 86 is divided into afirst fraction of the heated head stream 87A and a second fraction ofthe heated head stream 87B.

The ratio of the molar flow rate of the first fraction 87A to the molarflow rate of the second fraction 87B is greater than 2, and is inparticular for example comprised between 2 and 5.

The first fraction 87A is injected into the first compressor 32 drivenby the main turbine 26 to be compressed therein by pressure above 20bars.

The second fraction 87B is injected into the third compressor 41 to becompressed at a pressure greater than 20 bars and substantially equal tothe pressure at which the first fraction 87A is compressed in the firstcompressor 32.

Then, the compressed fractions 87A, 87B respectively resulting from thecompressors 32, 41 are brought together before being injected into thefirst air refrigerant 34. The reunited fractions 87A, 87B are cooledtherein to a temperature below 60° C., in particular to the ambienttemperature.

The compressed stream 88 thus obtained is injected into the secondcompressor 36, then into the second refrigerant 38 to form a compressedhead stream 90.

The stream 90 thus has a pressure greater than 40 bars, and inparticular substantially equal to 63.1 bars.

The compressed overhead stream 90 forms the methane-rich stream 12produced by the method according to the invention.

Its composition is advantageously 96.28% molar of methane, 2.37% molarof nitrogen, and 0.92% molar of ethane. It comprises more than 99.93% ofthe methane contained in the feed stream 16 and less than 5% of the C₂ ⁺hydrocarbons contained in the feed stream 16.

The second fraction 41B of the feed stream 16 is injected into thesecond dynamic expansion turbine 40 to be expanded at a second pressureP2 substantially equal to the pressure of the column 30 and to therebyform a second expanded feed fraction 91A.

The temperature of the second fraction 41B feeding the second dynamicexpansion turbine 40 is higher than the temperature of the turbine feedfraction 48 feeding the first dynamic expansion turbine 26, for exampleby at least 30° C.

Furthermore, the second pressure P2 is substantially equal to the firstpressure P1. The difference between the pressure P1 and the pressure P2is in particular less than 8 bars, advantageously less than 5 bars, andin particular less than 2 bars. The second expanded fraction 91A thushas a temperature below 0° C., and in particular in the vicinity of −25°C.

Then, the second fraction 91A is injected into the second heat exchanger28 to be cooled therein to a temperature below −70° C., and inparticular equal to −102.5° C., and to be partially condensed therein,by heat exchange with the head stream 84 and possibly with the columnfeed fraction 46, when it is present.

The second expanded fraction 91B from the second heat exchanger 28 formsa second reflux stream that is conveyed to the column 30 to be injectedtherein into the upper part of the level N12 for example situatedbetween the level N1 and the level N2, at the fourth stage starting fromthe top of the column.

Examples of temperatures, pressures, and molar flow rates of thedifferent streams are provided in Table 1 below.

TABLE 1 Temperature Pressure Flow rate Stream (° C.) (bara) (kmol/h) 12,90 40.0 63.1 13074 82 16.3 17.2 1926 16 30.0 62.0 15000 41A 30.0 62.012500 41B 30.0 62.0 2500 42 −26.7 61.0 12500 44 −26.7 61.0 11195 45−26.7 61.0 1305 46 −26.7 61.0 2460 48 −26.7 61.0 8735 49 −102.8 60.02460 52 −111.2 17.2 2460 54.56 −78.6 17.2 8735 60 −48.2 17.2 1305 84−104.8 17.0 13074 86 22.9 16.0 13074 87A 22.9 16.0 9387 87B 22.9 16.03687 88 40.0 24.3 13074 91A −25.5 18.2 2500 91B −102.5 17.2 2500

Table 2 below illustrates the power consumed by the compressor 36 as afunction of the flow rate of the second fraction 416 sent toward thesecond turbine 40.

TABLE 2 Flow rate Ethane toward turbine Turbine 26 Turbine 40 Compressor36 recovery 40 power power power (% moles) (kmol/h) (kW) (kW) (kW) 87.200 4381 0 14111 87.20 1600 3974 923 12996 87.20 2500 3574 1405 12244

The energy consumption of the method according to the invention, made upof the driving energy of the second compressor 36, is 12244 kW, versus14111 kW with the method from the state of the art according to U.S.Pat. No. 4,157,904 or 4,278,457, in which the same flow rate for theload to be treated is used and the same recovery achieved.

Relative to the state of the art, the method according to the inventiontherefore makes it possible to obtain a significant reduction in theconsumed power, while preserving high selectivity for the ethaneextraction.

A second piece of equipment 110 according to the invention is shown inFIG. 2. This piece of equipment 110 is intended to implement a secondmethod according to the invention.

The second method differs from the first method in that a bleed stream92 is removed from the compressed head stream 90.

The bleed stream 92 has a non-zero molar flow rate comprised between 0%and 35% of the molar flow rate of the compressed head stream 90 upstreamof the removal, the rest of the compressed head stream 90 forming thestream 12.

The bleed stream 92 is successively cooled in the first exchanger 20,then in the second exchanger 28, before being expanded in a third staticexpansion valve 94.

The stream 96, which, before expansion in the valve 94, is essentiallyliquid, has a liquid fraction greater than 0.8 after expansion.

The expanded bleed stream 96 from the third valve 94 is then injected inreflux near the head of the column 30 at a level N14 situated above thelevel N1 and advantageously corresponding to the first stage of thecolumn 30.

The temperature of the expanded bleed stream 96 before its injectioninto the column 30 is less than −70° C., and is advantageously equal to−113.5° C.

Examples of temperatures, pressures, and molar flow rates of thedifferent streams are provided in Table 3 below.

TABLE 3 Temperature Pressure Flow rate Stream (° C.) (bara) (kmol/h) 1240.0 63.1 12962 82 15.5 17.7 2038 16 30.0 62.0 15000 41A 30.0 62.0 1300041B 30.0 62.0 2000 42 −26.0 61.0 13000 44 −26.0 61.0 11676 45 −26.0 61.01324 46 −26.0 61.0 1865 48 −26.0 61.0 9811 49 −108.7 60.0 1865 52 −111.217.7 1865 54, 56 −76.9 17.7 9811 60 −46.9 17.7 1324 84 −110.7 17.5 1478686 25.1 16.5 14786 87A 25.1 16.5 11566 87B 25.1 16.5 3220 88 40.0 24.014786 90 40.0 63.1 14786 91A −24.4 18.7 2000 91B −105.0 17.7 2000 9240.0 63.1 1824 96 −113.5 17.7 1824

In one alternative (not shown), the second compressor 36 can comprisetwo compression stages separated by an aero-refrigerant.

The power consumed by the compressor 36 (single stage) as a function ofthe flow rate of the second feed stream fraction 41B is provided intable 4 below.

TABLE 4 Flow rate Ethane toward the Turbine 26 Turbine 40 Compressorrecovery turbine 40 power power 36 power % mole kmol/h kW kW kW 99.00 04421 0 15416 99.00 1000 4235 546 14510 99.00 1700 4051 928 14202 99.002000 3951 1100 14105 99.00 2500 3738 1415 14121

The second method according to the invention therefore makes it possibleto obtain extremely high ethane recovery rates, greater than 90%, and inparticular greater than 99%. This quasi-total recovery of the ethanecontained in the feed stream 16 can be obtained as in the methoddescribed in the U.S. Pat. No. 5,568,737, but with savings in terms ofconsumed power that can be greater than 8%, in the vicinity of 1300 kW.

A third piece of equipment 170 according to the invention is shown inFIG. 3.

The third piece of equipment 170 is intended to implement a third methodaccording to the invention.

The third method according to the invention differs from the firstmethod according to the invention in that the expanded feed fraction 54intended for the column 30 is at least partially injected in the secondheat exchanger 28 to be put in a heat exchange relationship therein withthe methane-rich overhead gas stream 84, with the second expanded feedfraction 91A from the second dynamic expansion turbine 40, andadvantageously with the column feed fraction 46, when the latter ispresent.

The fraction 54 is thus cooled to a temperature below −60° C., and inparticular substantially equal to −84° C. It is at least partiallycondensed to form the first cooled reflux stream 56.

The cooled reflux stream 56 is then injected into the middle part of thecolumn 30 at the level N2, as described above.

A bypass may be provided to inject part of the expanded fraction 54 intothe column 30 without going through the exchanger 28.

Examples of temperatures, pressures, and molar flow rates of thedifferent streams are provided in Table 5 below.

TABLE 5 Temperature Pressure Flow rate Stream (° C.) (bara) (kmol/h) 12,90 40.0 63.1 13071 82 17.4 17.7 1929 16 30.0 62.0 15000 41A 30.0 62.013340 41B 30.0 62.0 1560 42 −26.5 61.0 13440 44 −26.5 61.0 12049 45−26.5 61.0 1391 46 −26.5 61.0 2328 48 −26.5 61.0 9721 49 −102.2 60.02328 52 −110.5 17.7 2328 54 −77.5 17.7 9721 56 −84.4 17.6 9721 60 −47.517.7 1391 84 −104.2 17.5 13071 86 24.3 16.5 13071 87A 24.3 16.5 1071487B 24.3 16.5 2358 88 40.0 24.6 13071 91A −24.5 18.7 1560 91B −102.217.7 1560

A fourth piece of equipment 180 according to the invention is shown inFIG. 4. The fourth piece of equipment 180 is intended to implement afourth method according to the invention.

The fourth method according to the invention differs from the thirdmethod according to the invention, shown FIG. 3, in that a bleed stream92 is removed from the compressed head stream 90, then is successivelypassed through the first heat exchanger 20, then the second heatexchanger 28, as described in the second method according to theinvention.

The fourth method according to the invention is also similar to thethird method according to the invention.

A fifth piece of equipment 210 according to the invention is shown inFIG. 5. This fifth piece of equipment 210 is intended to implement afifth method according to the invention.

The fifth piece of equipment 210 is advantageously intended to increaseC₂ ⁺ recovery in an existing piece of equipment, in particular of thetype described in U.S. Pat. Nos. 4,157,904 and 4,278,457.

The existing equipment comprises the first heat exchanger 20, the firstseparating flask 22, the distillation column 30, the first compressor 32coupled to the first expansion turbine 26, and the second compressor 36.

The fifth piece of equipment 210 according to the invention alsocomprises a second dynamic expansion turbine 40, a third compressor 41,and a downstream separating flask 152 to collect the effluent from thesecond dynamic expansion turbine 40.

The equipment 210 also comprises an upstream heat exchanger 212, adownstream heat exchanger 214, and an auxiliary distillation column 216provided with an auxiliary bottoms pump 218.

The fifth piece of equipment 210 also comprises a fourth compressor 220inserted between two aero-refrigerants 222A, 222B.

The fifth piece of equipment 210 also comprises a downstream separatingflask 152, arranged downstream of the second turbine 40.

The fifth method according to the invention differs from the firstmethod according to the invention in that the feed current 16 is alsoseparated into a third fraction 224 of the feed current that is injectedinto the upstream heat exchanger 212, before being mixed with the firstfraction 41A from the exchanger 20 to form the first cooled fraction 42.

The ratio of the molar flow rate of the third fraction 224 to the molarflow rate of the feed stream 16 is greater than 5%.

In this way, the fifth method according to the invention differs fromthe first method according to the invention in that the second feedfraction 91A, cooled and partially liquefied, is injected into thedownstream separating flask 152.

This fraction 91A is separated in the downstream separating flask 152into a second liquid bottoms stream 154 and a second gas head stream156.

The second liquid bottoms stream 154 is injected into a fourth staticexpansion valve 157 to be expanded there substantially at the pressureof the column 30 and to form a second expanded bottoms stream 158.

Unlike the first method according to the invention described above, thesecond head stream 156 from the downstream separating flask 152 isinjected into the downstream heat exchanger 214 to be cooled therein toa temperature below −70° C. and form a second cooled head stream 225.

The second cooled head stream 225 is injected into the auxiliary column216 at a lower stage E1.

The column 216 has a theoretical number of stages lower than thetheoretical number of stages of the column 30. This number of stages isadvantageously comprised between 1 and 7. The auxiliary column 216operates at a pressure substantially equal to that of the column 30.

The expanded bottoms stream 158 obtained after expansion of the secondbottoms stream 154 in the valve 157 is injected into the column 30 alevel N1 advantageously corresponding to the first stage from the top ofthe column 30.

A first part 226 of the fraction 52 expanded in the valve 50 is injectedinto the auxiliary column 216 at a stage E3 situated above the level E1.A second part 228 of the fraction 52 is injected directly into thecolumn 30 at the level N1, after mixing with the stream 158.

The auxiliary column 216 produces a methane-rich auxiliary head stream230 and an auxiliary bottoms stream 232.

The auxiliary head stream 230 is mixed with the methane-rich head stream84 produced by the distillation column 30.

The bottoms stream 232 is pumped by the auxiliary pump 218 to form acooled reflux stream 234 that is injected into the column 30 aftermixing with the stream 158.

The stream 234 therefore constitutes a cooled reflux stream that isobtained from a part of the expanded fraction 91A from the seconddynamic expansion turbine 40, after separation of that effluent.

The mixture 235 of the head streams 84 and 230 is separated into a firstmajority head stream fraction 236 and the second minority head streamfraction 238.

The ratio of the molar flow rate of the majority fraction 236 to theminority fraction 238 is greater than 1.5.

The majority fraction 236 is successively injected into the second heatexchanger 28, then into the first heat exchanger 20, so as to form theheated head stream 86.

The second head stream fraction 238 is passed into the downstream heatexchanger 214 countercurrent to the second head stream 156 to be heatedthere to a temperature above −50° C. and form a second heated fraction240.

The second heated fraction 240 is then separated into a return stream242 and decompression stream 244.

The return stream 242 is reinjected into the first head stream fraction236, downstream of the second exchanger 28 and upstream of the firstexchanger 20 to partially form the heated head stream 86.

The recompression stream 244 is then injected into the upstreamexchanger 212 to cool the third fraction of the feed stream 224. Thestream 244 heats up to a temperature above −10° C. to form a heatedrecompression stream 246.

A first part 248 of the recompression stream 246 is mixed with the firstfraction of the head stream 86, downstream of the first heat exchanger20 to form the heated head stream 87A.

A second part 250 of the recompression stream 246 is injected into thethird compressor 41, then the aero-refrigerant 222A, before beingrecompressed in the fourth compressor 220 and injected into theaero-refrigerant 222B.

The second compressed part 252 from the aero-refrigerant 222B has atemperature below 60° C., and in particular substantially equal to 40°C., and a pressure greater than 35 bars, and in particular equal to 63.1bars.

This first compressed part 252 is mixed with the compressed head stream90 to form the methane-rich stream 12.

The fifth piece of equipment 210 and the fifth method according to theinvention therefore make it possible to increase the C₂ ⁺ hydrocarbonrecovery rate in an existing piece of equipment of the state of the art,without having to modify the existing pieces of the equipment, and inparticular while keeping the heat exchangers 20 and 28, the column 30,the compressors 32, 36 and the turbine 26 identical, and using the inputalready present on the column 30.

To keep the existing equipment intact and improve the C₂ ⁺ recovery, thepressure of the column 30 has been slightly decreased. Withoutcountermeasure, this decrease would have caused an increase in the powerof the compressor 36.

However, the addition of the compressor 220 makes it possible to offsetthis problem. Furthermore, the flow rate through the existing turbine 26and its power have not been increased relative to the existing unit.

This piece of equipment nevertheless makes it possible to obtain, withan excellent output, a much greater ethane recovery than that observedin the state of the art. A sixth piece of equipment 270 according to theinvention is shown in FIG. 6.

This sixth piece of equipment 270 is intended to implement a sixthmethod according to the invention.

The sixth method according to the invention differs from the fifthmethod according to the invention in that a bleed stream 92 is removedfrom the compressed methane-rich head stream 90, advantageously upstreamof the injection point of the second compressed part 252 in the stream90.

The bleed stream 92 is reinjected into the column 30 at a head levelN14. Unlike the fifth method according to the invention, the second part228 of the fraction 52 and the expanded bottoms stream 158 are injectedinto the column at a level N5 situated under the head level N14 andabove the level N2.

The implementation of the sixth method according to the invention isalso similar to that of the fifth method according to the invention.

To keep the C₂ ⁺ recovery of the existing unit, the pressure of thecolumn 30 is slightly decreased. The presence of the new compressor 220makes it possible to keep the power of the second compressor 36identically, despite the increased flow rate of the feed stream 16.

Furthermore, the capacity of the first dynamic expansion turbine 26 hasbeen kept constant. The second dynamic expansion turbine 40 is used tohandle the added capacity. The presence of an auxiliary column 216 alsomakes it possible to avoid flooding of the column 30 during the flowrate increase.

The sixth piece of equipment according to the invention makes itpossible to preserve an ethane recovery greater than or equal to 99%, atemperature and pressure of the feed stream 16 that are substantiallyidentical. Likewise, the pressure losses allocated in the equipment, theefficiencies of the plates in the column 30 and the position of thebleeds, the maximum methane specification of the bottoms stream 82 ofthe column 30, the efficiencies of the turbines and compressors, thepower of the second compressor 36 and the existing turbine 26, and theheat exchange coefficients of the existing exchangers 20 and 28 are keptidentical.

In one alternative (shown in broken lines in FIG. 1), which can apply toeach of the embodiments of FIGS. 1 to 6, the second fraction 41B of thefeed stream is removed in the first exchanger 20 and not upstream of thelatter. The second fraction 41B is therefore partially cooled and ispartially liquefied in the first heat exchanger 20.

The second fraction 41B from the first heat exchanger 20 is thenpossibly injected into an upstream separating flask 250. It is thenseparated in the upstream separating flask 250 into a second bottomsliquid fraction 252 and a second gas head fraction 254. The secondbottoms fraction 252 is expanded in a static expansion valve 256 to apressure below 40 bars and substantially equal to the pressure of thecolumn 30.

The second expanded bottoms fraction 258 is then injected into thecolumn 30, advantageously between the level N11 and the level N8.

The second head fraction 254 is injected into the second dynamicexpansion turbine 40 to form the second expanded feed fraction 91A.

This arrangement with an upstream separating flask also applies to thecase where the feed stream 16 contains a liquid fraction.

In another alternative (not shown) of the embodiments of FIGS. 2, 4 and6, the equipment comprises a bypass valve for part of the bleed stream92 to divert that part upstream of the first dynamic expansion turbine26.

In this alternative method, an extra cooling stream is removed from thebleed stream obtained after its passage in the first heat exchanger 20.The extra cooling stream is reinjected upstream of the turbine 26,either in the head stream 44, or upstream of the separating flask 22 inthe cooled feed stream 42.

In another alternative (not shown) of the embodiments of FIGS. 1 to 8,the equipment comprises a plurality of first exchangers 28, each beingintended to receive a fraction of the head stream 84 and another stream.

The head stream 84 is then divided into a plurality of fractionscorresponding to the number of second exchangers 28.

Each second exchanger 28 can then put into a heat exchange only twoflows each including a fraction of the head stream 84 and, respectively,the first expanded feed fraction 54, the second expanded feed fraction91A, and, if applicable, the column feed fraction 46 and/or the removalfraction 92.

In another alternative (not shown) of the embodiments of FIGS. 1 to 6, areboiling stream is removed from the distillation column at a removallevel. The reboiling stream is then put into a heat exchangerelationship with at least one part of the second expanded fraction 91Afrom the dynamic expansion turbine 40, and potentially with the firstexpanded fraction 54 of the first turbine 26.

This placement in a heat exchange relationship can be done within thesecond heat exchanger 28.

In still another alternative (not shown), an auxiliary expansion streamis removed from the methane-rich overhead stream 86 from the first heatexchanger 20. This auxiliary expansion stream is injected into anauxiliary dynamic expansion turbine, separate from the first dynamicexpansion turbine 26 and the second dynamic expansion turbine 40. Theexpanded stream from the auxiliary turbine is reinjected into themethane-rich overhead stream, before its passage in the first heatexchanger 20, to form an extra cooling stream of the first heatexchanger 20.

More generally, the entire head stream 44 from the first separatingflask 22 can form the turbine feed fraction 48. The method according tothe invention is then provided with no separation of the head stream 44.

1. A method for producing a methane-rich stream and a C2⁺hydrocarbon-rich stream from a feed stream containing hydrocarbons, saidmethod comprising: separating the feed stream into a first fraction ofthe feed stream and at least one second fraction of the feed stream;cooling the first fraction of the feed stream in a first heat exchangerto produce a cooled first fraction, said separating of the feed streamoccurs upstream of the cooling of the first fraction of the feed stream;injecting the cooled first fraction of the feed stream in a firstseparating flask to produce a light head stream and a heavy bottomsstream; expanding a turbine feed fraction formed from the light headstream in a first dynamic expansion turbine to a first pressure andinjecting at least part of the first expanded fraction coming from thefirst turbine into a first distillation column; expanding the wholeheavy bottoms stream to form an expanded bottoms stream and injectingthe expanded bottoms stream into the first distillation column withoutgoing through the first heat exchanger between the first separatingflask and the first distillation column; recovering a bottoms stream atthe bottom of the first distillation column, the C2⁺ hydrocarbon-richstream being formed from the bottoms stream; recovering and heating amethane-rich overhead stream from the first distillation column;compressing at least one fraction of the methane-rich overhead stream inat least a first compressor coupled to the first dynamic expansionturbine and in at least one second compressor; injecting at least partof the second fraction of the feed stream into a second dynamicexpansion turbine, separate from the first dynamic expansion turbine;expanding the at least part of the second fraction of the feed stream inthe second dynamic expansion turbine to a second pressure, to form asecond expanded fraction coming from the second dynamic expansionturbine, the second pressure being substantially equal to the firstpressure; injecting the second expanded fraction coming from the seconddynamic expansion turbine into a downstream separating flask to form asecond gas head stream and a second liquid bottoms stream; cooling thesecond gas head stream to form a cooled reflux stream; and injecting thecooled reflux stream into the first distillation column.
 2. The methodaccording to claim 1, wherein said method includes injecting the firstexpanded fraction from the first dynamic expansion turbine into a secondheat exchanger to be cooled and partially liquefied therein, the firstcooled expanded fraction forming an additional cooled reflux stream, themethod including the injection of the additional cooled reflux streaminto the first distillation column.
 3. The method according to claim 1,wherein said method further comprises injecting at least part of thesecond expanded fraction from the second dynamic expansion turbine intoan auxiliary column, and forming a cooled reflux stream from the bottomsstream of the auxiliary column.
 4. The method according to claim 1,wherein said method further comprises optionally, partially condensingthe second fraction of the feed stream; injecting the second fraction ofthe feed stream into an upstream separating flask to form a second gasfraction and a second liquid fraction; injecting the second gas fractioninto the second dynamic expansion turbine; injecting the second liquidfraction, after expansion, into a lower part of the first distillationcolumn.
 5. The method according to claim 1, wherein said method furthercomprises injecting an entirety of the of the second fraction of thefeed stream into a second dynamic expansion turbine, separate from thefirst dynamic expansion turbine, without cooling between the step forseparating the feed stream and the step of injecting the second fractionof the feed stream into the second dynamic expansion turbine; expandingthe entirety of the second fraction of the feed stream in the seconddynamic expansion turbine to a second pressure, to form a secondexpanded fraction coming from the second dynamic expansion turbine, thesecond pressure being substantially equal to the first pressure
 6. Themethod according to claim 1, wherein said method further comprisesremoving a secondary compression fraction in the methane-rich overheadstream, before the passage of a fraction of the methane-rich overheadstream in the first compressor, passage of the secondary fraction in athird compressor coupled to the second dynamic expansion turbine;injecting the compressed secondary fraction from the third compressorinto the fraction of the compressed overhead stream, downstream of thefirst compressor.
 7. The method according to claim 1, wherein the secondcompressor comprises a first compression stage, at least one secondcompression stage, and a refrigerant inserted between the firstcompression stage and the second compression stage, the method includinga step for passage of the compressed overhead stream from the firstcompressor successively in the first compression stage, the refrigerant,then the second compression stage.
 8. The method according to claim 1,wherein at least part of the second expanded fraction from the seconddynamic expansion turbine, at least one fraction of the overhead stream,and possibly the first expanded fraction hum the first dynamic expansionturbine, are placed in a heat exchange relationship.
 9. The methodaccording to claim 1, wherein said method further comprises dividing thelight head stream into the turbine feed fraction and a column feedfraction; cooling and at least partially condensing the column feedfraction in a second heat exchanger to form a cooled feed fraction;expanding and at least partially injecting the cooled column feedfraction into the first distillation column; and at least part of thesecond expanded fraction from the second dynamic expansion turbine andthe column feed fraction advantageously being placed in a heat exchangerelationship.
 10. The method according to claim 9, wherein at least afraction of the overhead stream and at least one part of the secondexpanded fraction from the second dynamic expansion turbine are placedin a heat exchange relationship in a downstream heat exchanger separatefrom the second heat exchanger.
 11. The method according to claim 1,wherein said method further comprises removing a bleed stream from theoverhead stream; cooling the bleed stream at least in the first heatexchanger and injecting the cooled bleed stream into the firstdistillation column; and optionally, heat exchange of the bleed streamwith at least part of the second expanded fraction from the secondturbine.
 12. The method according to claim 1, wherein said methodfurther comprises removing a reboiling stream in the first distillationcolumn at a removal level; putting the reboiling stream in a heatexchange relationship with at least part of the second expanded fractioncoming from the second dynamic expansion turbine to cool and at leastpartially liquefy the part of the expanded second fraction coming fromthe second dynamic expansion turbine; and optionally, placement in aheat exchange relationship with the first expanded fraction from thefirst turbine; reinjecting the reboiling stream into the firstdistillation column at a level below the removal level.
 13. The methodaccording to claim 1, wherein said method further comprises removing anextra cooling stream from the methane-rich overhead stream or from thestream formed from the methane-rich overhead stream or a stream formedfrom the methane-rich overhead stream; expanding and injecting theexpanded extra cooling stream into a stream circulating upstream of thefirst expansion turbine, advantageously in the first fraction of thecooled feed stream or in the turbine feed fraction.
 14. The methodaccording to claim 1, wherein said method further comprises passage ofthe methane-rich overhead stream in the first heat exchanger; removal ofan auxiliary expansion stream in the methane-rich overhead stream, afterits passage in the first heat exchanger; dynamic expansion of theauxiliary expansion stream in an auxiliary dynamic expansion turbine;injecting the expanded stream from the auxiliary dynamic expansionturbine into the methane-rich overhead stream, before its passage in thefirst heat exchanger.
 15. An equipment for producing a methane-richstream and a C2⁺ hydrocarbon-rich stream from a feed stream containinghydrocarbons in accordance with the method as recited in claim 1, theequipment comprising: means for separating the feed stream into a firstfraction of the feed stream and at least one second fraction of the feedstream; a first heat exchanger to cool the first fraction of the feedstream, said separating of the feed stream occurs upstream of thecooling of the first fraction of the feed stream; means for injectingthe first cooled feed fraction into a first separating flask to producea light head stream and a heavy bottoms stream; a first dynamicexpansion turbine and means for injecting a turbine feed fraction formedfrom the light head stream into the first dynamic expansion turbine soas to expand the turbine feed fraction to a first pressure; a firstdistillation column; means for injecting at least part of the firstexpanded fraction into the first turbine in the first distillationcolumn; means for expanding the whole heavy bottoms stream to form anexpanded bottoms stream and means for injecting at least part of theexpanded bottoms stream into the first distillation column, the meansfor injecting the expanded bottoms stream being configured so that thebottoms stream does not pass through the first heat exchanger betweenthe first separating flask and the first distillation column; means forrecovering a bottoms stream at the bottom of the first distillationcolumn, the C2⁺ hydrocarbon-rich stream being formed from the bottomsstream; means for recovering and heating a methane-rich overhead streamfrom the first distillation column, at least one first compressorcoupled to the first dynamic expansion turbine and at least one secondcompressor to compress at least one fraction of the methane-richoverhead stream; a means for injecting at least part of the of thesecond fraction of the feed stream into a second dynamic expansionturbine, separate from the first dynamic expansion turbine, andinjecting the at least part of the second fraction of the feed streaminto the second dynamic expansion turbine to form a second expandedfraction from the second dynamic expansion turbine at a second pressure,the second dynamic expansion turbine being arranged so that the firstpressure is substantially equal to the second pressure; and means forinjecting the second expanded fraction coming from the second dynamicexpansion turbine into a downstream separating flask to form a secondgas head stream and a second liquid bottoms stream, means for coolingthe second gas head stream to form a cooled reflux stream, and means forinjecting the cooled reflux stream into the first distillation column.16. The equipment according to claim 15, wherein said equipment furthercomprises an auxiliary column; means for injecting at least part of thesecond expanded fraction from the second dynamic expansion turbine intothe auxiliary column; and means for forming the cooled reflux streamfrom the bottoms stream of the auxiliary column.
 17. The methodaccording to claim 1, wherein the heavy bottoms stream issuing from thefirst separating flask is expanded in an expansion valve to form theexpanded bottoms stream, the expanded bottoms stream being injected inthe first distillation column without passing through the first heatexchanger between the outlet of the expansion valve and the injectioninto the first distillation column.
 18. The method according to claim 1,wherein no stream issuing from the second dynamic expansion turbineenters into heat exchange in a heat exchanger with the first fraction ofthe feed stream, upstream of the distillation column.
 19. A method forproducing a methane-rich stream and a C2⁺ hydrocarbon-rich stream from afeed stream containing hydrocarbons, said method comprising: separatingthe feed stream into a first fraction of the feed stream and at leastone second fraction of the feed stream; cooling the first fraction ofthe feed stream in a first heat exchanger to produce a cooled firstfraction, said separating of the feed stream occurs upstream of thecooling of the first fraction of the feed stream; injecting the cooledfirst fraction of the feed stream in a first separating flask to producea light head stream and a heavy bottoms stream; expanding a turbine feedfraction formed from the light head stream in a first dynamic expansionturbine to a first pressure and injecting at least part of the firstexpanded fraction coming from the first turbine into a firstdistillation column; expanding the whole heavy bottoms stream to form anexpanded bottoms stream and injecting the expanded bottoms stream intothe first distillation column without going through the first heatexchanger between the first separating flask and the first distillationcolumn; recovering a bottoms stream at the bottom of the firstdistillation column, the C2⁺ hydrocarbon-rich stream being formed fromthe bottoms stream; recovering and heating a methane-rich overheadstream from the first distillation column; compressing at least onefraction of the methane-rich overhead stream in at least a firstcompressor coupled to the first dynamic expansion turbine and in atleast one second compressor; injecting at least part of the secondfraction of the feed stream into a second dynamic expansion turbine,separate from the first dynamic expansion turbine, without coolingbetween the step for separating the feed stream and the step ofinjecting the second fraction of the feed stream into the second dynamicexpansion turbine; expanding the at least part of the second fraction ofthe feed stream in the second dynamic expansion turbine to a secondpressure, to form a second expanded fraction coming from the seconddynamic expansion turbine, the second pressure being substantially equalto the first pressure; and injecting at least part of the secondexpanded fraction from the second dynamic expansion turbine into anauxiliary column, and forming a cooled reflux stream from the bottomsstream of the auxiliary column and injecting the cooled reflux streaminto the first distillation column.